Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session C2: Topological Insulators |
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Chair: Joe Poon, University of Virginia Room: Salon C |
Thursday, November 10, 2016 1:30PM - 2:00PM |
C2.00001: Conductance of a superconducting Coulomb blockade nanowire at finite temperature Invited Speaker: Ching-Kai Chiu By applying a magnetic field, a superconducting proximity nanowire in the presence of spin-orbital coupling can pass through topological phase transition and possess Majorana bound states on the ends. One of the promising platforms to detect the Majorana modes is a coulomb blockade island by measuring its two-terminal conductance (S. M. Albrecht et al., Nature (London) 531, 206 (2016)). Here, we study the transportation of a single electron across the superconducting Coulomb blockade nanowire at finite temperature to obtain the general conductance equation. By considering all possible scenarios that Majorana modes appear in the nanowire, we compute the nanowire conductance as the magnetic field and the gate voltage of the nanowire vary. The oscillation behavior of the conductance peak is temperature independent and the amplitude oscillation of the conductance peak decreases as the magnetic field increases. [Preview Abstract] |
Thursday, November 10, 2016 2:00PM - 2:30PM |
C2.00002: Spin filtering using PN junctions in topological insulators Invited Speaker: Avik Ghosh 3D topological insulators share a lot of properties with other 2D Dirac cone systems such as graphene. In both systems, the Dirac bands can be labeled with an index that corresponds to the phase of its eigenfunction (pseudospins representing bonding-antibonding combinations of the dimer pz orbitals in graphene, vs real spins in 3D TIs). The locking of momentum with these phases makes it possible to filter the latter simply by gating the former. For graphene PN junctions, we expect rich chiral physics such as Klein tunneling, negative index behavior, and Veselago lensing that should also show up in Bi2Se3 topological insulators. The ability to steer or collimate the electrons through angular filtering (ie, gate geometry alone), for instance using a PN junction, would allow us to open gate-tunable transport gaps that can be used to filter the spins, amplify the torques and turn off the overall device. We present analytical, numerical and experimental demonstrations of pseudospin filtering in graphene, and show how we can use these properties for a cascaded sequence of angled junctions in order to turn it off without compromising the electron mobility. The analogous physics can be studied more directly on a topological insulator using a ferromagnetic tip. Accordingly, we can use a single PN junction to amplify the charge to spin conversion rate (analogous to a spin Hall angle, except it is tunable from 0 to 30). This tunability can then be used to amplify the torque at the injection side and the polarization on the transmitted side, and build spin based logic circuits with isolation and gain. (Ref: Science 353, 6307, 2016; PRL 114, 176801, 2015; ACS Nano 7, 9808, 2013) [Preview Abstract] |
Thursday, November 10, 2016 2:30PM - 3:00PM |
C2.00003: Topological strings and fractional pumping in superconductors Invited Speaker: Jeffrey Teo Quantum flux vortices are topological line defects of the pairing order parameter in a superconductor in three dimensions. On the other hand, chiral gapless Majorana fermions live along another kind of topological line defects that involve non-trivial spatial modulations of the Bogoliubov-de Gennes Hamiltonian. Topological strings are combinations of these two types of line defects. I theoretically describe the different fractional pumping processes through linking topological strings in superconducting Dirac semimetals. [Preview Abstract] |
Thursday, November 10, 2016 3:00PM - 3:30PM |
C2.00004: Unconventional superconductivity in bilayer transition metal dichalcogenides Invited Speaker: Chaoxing Liu Two dimensional layered materials, such as graphene and transition metal dichalcogenides, have revealed rich physical phenomena due to the interplay between different degrees of freedom, including spin, valley and layer degrees. In this talk, we will discuss unconventional superconductivity in bilayer transition metal diachalcogenides and show how multiple degrees of freedom in this system can lead to unconventional superconductivity. We find that intra-layer singlet pairings (A$_{\mathrm{1g}}$ and A$_{\mathrm{1u}}$ pairing) and inter-layer triplet pairing (E$_{\mathrm{u}}$ pairing) are possible to be stable in the phase diagram, depending on the relative strength of intra-layer and inter-layer interactions. Furthermore, by applying an in-plane magnetic field, we predict that the superconducting state with intra-layer singlet pairing will evolve to an inhomogeneous helical Fulde-Ferrell-Larkin-Ovchinnikov phase due to the presence of a new linear gradient term, which also linearly depends on magnetic fields, in the Landau free energy. We also discuss the experimental relevance of our results and possible experimental signatures to identify the helical state. Reference: [1] Unconventional superconductivity in bilayer transition metal dichalcogenides, Chao-Xing Liu, arXiv: 1608.04139, 2016. [Preview Abstract] |
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